Let a shader declare a color the sprite sets (#298)

A shader could only ask its sprites for numbers. A tint, an outline
colour or a glow colour had to be built from three Property nodes.

- New node Color property next to Property: Name and Default (a
  colour, white unless picked), output `color`. It becomes a colour
  row below the Shader dropdown and a vec3 uniform in the program.
- Number and colour properties share one set of names. A clash is
  the existing "Another property is named" problem.
- Like Color it cannot feed the Vertex output.
- Placed from the palette it is called tint, then tint2.
- The preview in the Shader tab shows a colour field for it. Like
  the sliders it starts at the sprite's value and never writes into
  the project.
- `declaredRows` takes the row builder, so the particle graph keeps
  its number rows unchanged.

Tests:
- Gate: 222 files, 3452 tests (3445 + 7)
- e2e 28: 89 checks (28l-v: default colour drawn, then the colour
  the sprite sets)
- e2e total 1704, counted (1703 + 1)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/core/shaders.test.ts

@@ -215,9 +215,9 @@ describe('compileShader', () => {
     expect(build.reason).toBe('');
     const compiled = build.compiled!;
     expect(compiled.uniforms).toEqual([
-      { name: 'brightness', default: 1 },
-      { name: 'contrast', default: 1 },
-      { name: 'saturation', default: 1 },
+      { name: 'brightness', kind: 'number', default: 1 },
+      { name: 'contrast', kind: 'number', default: 1 },
+      { name: 'saturation', kind: 'number', default: 1 },
     ]);
     const { fragment } = compiled;
     for (const name of ['brightness', 'contrast', 'saturation'])